Process for the production of phosphate fertilizers



I Patented Feb. 4, 1941 UNITED STATES PROCESS FOR THE PRODUCTION OF PHOSPHATE FERTILIZER-S Otto Johannsen and Karl-Heinz Hennenberger,

Volklingen, Saar,

Germany,

assignors to Rochlingsche Eisenund Stahlwerke, Gesellschaft mit beschrinkter Haftnng, Volklingen, Saar, Germany, a limited-liability company No Drawing. Application October 21, 1938, Serial No. 236,298. In Germany October 23, 1937 4 Claims.

This invention relates to an improvement in the process for the production of phosphate fertilizers according to our patent application Ser. No. 137,552. In this process phosphate fertilizers 5 are produced by meltingtogether mineral phosphate with the soda slag obtained at the treatment of pig iron with soda and soda containing substances in furnaces such as a drumor revolving furnace. The lining of the furnace is strong- 1y attacked by the molten mass. Even first quality chamotte bricks are completely corroded by the molten mass in a very short time. It has already been proposed to employ for the lining magnesite bricks which are distinguished by their resistance against slags of the most various kind, but it has been found that even very dense kinds of magnesite bricks were completely corroded after a service of only few hours.

Reflections and experiments did lead to the surprising result that stamped clay and stamped bodies consisting of magnesite or dolomite with tar as binding medium are excellently suited, in opposition to burnt magnesite bricks, for lining phosphate melting furnaces. Apparently a layer forms on the burnt magnesite bricks which, owing to the chemical reaction with the molten phosphate, possesses another expansion capability than the original brick, so that a driving force is exerted which leads to foliations. Compared herewith the stamped lining seems to preserve its elasticity.

7 It has already become known to line with a tardolomite-lining Thomas converters and open hearth furnaces. In the Thomas and open hearth process slags free from alkali and highly basic, that is very rich in lime, are formed which corrode only very little the dolomite or magnesite linings of any kind. In contradiction to this,

the fused phosphate fertilizer is a nearly neutral product with a high content of alkali, which carrodes magnesite bricks in an astonishingly high degree, but attacks tar-dolomite lining very little. It is therefore not possible to conclude from the stability of a tar-dolomite-lining against Thomas or open hearth slags how such lining would behave against fused phosphate.

The lining of the furnace is practically carried out in the manner known from the Thomas converters and open hearth furnaces in that the hot mixture of dolomite or magnesite and tar is stamped behind a template of wood or sheet metal plate and then the lining is burnt-in with a light fire. The furnace may, however, also be lined with pressed bricks produced from the 5 above mentioned mixtures.

It has been found that the resistance of such linings is substantially higher than that of all the linings which have been proposed up to the present. The expenses for renewing the lining 10 are comparatively little, the time required herefore amounts only to a few days including the breaking off of the old lining. An advantage is further that the fused phosphates produced on the lining according to the invention possess a 15 very good solubility of phosphoric acid.

A revolving furnace of a length of 12 m. and of 1.3 or 2.2 m. diameter equipped with a widening for holding the molten mass was strongly stamped with a heated mixture of dolomite and 2 tar with the aid of compressed air stampers. The dolomite employed was sharply burnt and had a grain size of 5 to 8 mm. The addition of tar amounted to 8 to 10%. It had been produced at the coking of Saar coal in the coke oven, pos- 25 sessed a specific gravity of 1.23 and an oil content of 22%. The residue fromeoking amounted to 23%. The furnace has been used for the production of fused phosphate from 1 part by weight pebble phosphate and 1 part by weight soda slag 3o from the desulphurization of Thomas pig iron poor in manganese. Every day 26 tons of raw mixture were worked. After the furnace had been used during '21 days, the lining was destroyed at the points which were exposed to the 3 action of the fused mass and to the mechanical action of the blooms contained therein and produced by welding of the iron granules. The damaged points were repaired without cooling of the furnace with the same mixture of tar and 40 dolomite. The oven worked in this state for another ten days, and the hottest part of the lining was then renewed on alength of 3 m. The' lining remainedinthefurnaceat the points which 45 had been less heated. This part of the lining has lasted already over more than 2% months.

In the following table the durability of the new lining is compared with that of the linings of known kind. The average andmaximum dissolv-. 50

ing degree of the phosphoric acid is also indi ceted.

1. A process for the production of phosphate fertilizers by melting together phosphate rock with the soda slag obtained by treating pig iron with soda ash and soda containing mixtures in a rotary furnace, consisting in melting the charge on a lining made by stamping a mixture of calcined dolomite with tar.

2. A process for the production of phosphate fertilizers by melting together phosphate rock with the soda slag obtained by treating pig iron with soda ash and soda containing mixtures in a rotary furnace, consisting in melting the charge on a lining built up of bricks pressed from a mixture of dolomite with tar.

3. A process for the production of phosphate fertilizers by melting together phosphate rock with the soda slag obtained by treating pig iron with soda ash and soda containing mixtures with an addition of common salt in a rotary furnace, consisting in melting the charge on a lining made by stamping a mixture of calcined dolomite with tar.

4. A process for the production of phosphate fertilizers by melting together phosphate rock with the soda slag obtained by treating pig iron with soda ash and soda containing mixtures with an addition of common salt in a rotary furnace,

consisting in melting the charge on a lining built up of bricks pressed from a mixture of dolomite with tar.

O'I'IO JOI-IANNSEN. KARL-HEINZ HENNENBERGER. 

